1. Field of the Invention
The present invention relates to an electrical current sensor able to detect a current with high accuracy over a wide measuring range.
2. Description of the Related Art
In an electric vehicle, a motor is driven using electricity generated by an engine, and a magnitude of a current for driving the motor is detected by, for example, an electrical current sensor. As the current sensor, there is a magnetic proportional current sensor and a magnetic balance current sensor. In the case of the magnetic proportional current sensor, a magnetic field proportional to a current being measured, passes through a core gap due to magnetic force lines generated in a magnetic core, and a magnetic detection element converts the magnetic field into a voltage signal to thereby generate an output voltage proportional to the current to be measured. Meanwhile, in the case of the magnetic balance current sensor, when the current to be measured flows in the magnetic balance current sensor, an output voltage is generated in a magnetic detection element due to a magnetic field according to the current, and a voltage signal output from the magnetic detection element is converted into an electrical current to be fed back to a feedback coil, and a magnetic field (a canceling magnetic field) generated by the feedback coil and a magnetic field generated by the current to be measured are canceled out by each other so that the magnetic field is always zero. In this instance, the magnetic balance current sensor voltage-converts the feedback current flowing in the feedback coil to thereby be extracted as an output.
The magnetic balance current sensor using a Giant Magneto Resistance (GMR) element may have a more complex configuration than that of the magnetic proportional current sensor, but measures a current to be measured over a wide measuring range. However, it is necessary that accuracy of the measurement is uniform over the measuring range, and the number of turns of the feedback coil is generally fixed and selected so as to use the appropriate number of turns considering a measuring range or a consumption current according to applications, and therefore it is difficult to simultaneously perform measurement of a large current of a rated operating condition and measurement of a very small current such as a sleep current of a system with high accuracy. On the other hand, in the magnetic proportional current sensor, it is possible to perform measurement of the very small current with high accuracy by setting a narrow measuring range, but when assuming that measurement of a large current is also to be performed, it is necessary to extend the measuring range so that a GMR element is not saturated. However, when extending the measuring range, the resolution when the current to be measured is small is reduced, and it is difficult to perform measurement of the very small current with high accuracy.
With respect to such a problem, in order to perform current measurement with high accuracy over a wide detection range, a method in which a magnetic proportional current sensor using a Hall element and a magnetic balance current sensor using a Hall element are arranged, and used by switching them according to a magnitude of a current to be measured, has been disclosed (for example, see Japanese Unexamined Patent Application Publication No. 2007-78416).
However, in the technique disclosed in Japanese Unexamined Patent Application Publication No. 2007-78416,two different types of current sensors have to be provided. Due to this, space saving and cost reduction cannot be achieved, and manufacturing processes becomes complicated. In addition, in the technique disclosed in Japanese Unexamined Patent Application Publication No. 2007-78416,magnetic balance in the magnetic balance current sensor which is not used collapses when the current to be measured is large, and therefore magnetic saturation is caused when a GMR element is used as a magnetic detection element. Therefore, in the technique disclosed in Japanese Unexamined Patent Application Publication No. 2007-78416,it is difficult for the magnetic detection element to perform measurement with high accuracy over a wide measuring range.